The present invention relates to an anchor rod for a synthetic resin adhesive anchor having a shaft, which has a plurality of areas arranged in axial succession, the surfaces of which are low-friction with respect to synthetic resin mortar.
One anchor rod of this type is known, for example, from EP 0 356 425 B 1. Anchor rods of the type in question have the advantage that during hardening of the synthetic resin mortar a shell of mortar is formed, relative to which the anchor rod can be shifted in an axial direction when the mortar shell cracks or when the interior diameter of the mortar shell changes when a dynamic fracture occurs. The axial movement of the anchor rod then results in the build-up of a corresponding expansion pressure.
The known products have the shortcoming, however, that a protective grating must be provided for practical implementation, to prevent damage to the coating on the cone areas during insertion of the anchor rod into the borehole.
From DE 38 23 863 A1 an anchor rod is known with areas in the region of the cone that are formed at an angle to the longitudinal axis. However, this anchor rod is not suitable for creating a desired splitting zone in the region of the shaft.
From DE 196 34 912 A1 an anchor rod comprising a shaft with a spiral configuration is known, by which a splitting of the borehole can also not be attained, and the use of which creates problems if the anchor mortar contains coarse aggregates.
Based on the above, it is the aim of the present invention to improve an anchor rod of the above type in such a way that it becomes possible to insert the anchor rod into the borehole without additional protective measures while maintaining the advantage of attaining high pull-out forces even when cracks develop in the concrete.
This aim is met with areas that are formed and, viewed in a circumferential direction, arranged such that a desired splitting zone is created in the transition region of two adjacent areas of this type, with a friction-increasing coating provided.
The cross-section of the shaft in the region of the areas is preferably such that the areas approximately correspond to a triangle or square inscribed in the cylindrical envelope curve or in the borehole diameter.
In a further embodiment of the invention the sides of the triangle or square may be shaped concave toward the longitudinal center axis.
Cone sections may advantageously be formed on the shaft in such a way that each of the areas is formed on a cone section of the shaft, superimposed on the same.
It has proven particularly advantageous that the axial and/or radial size of the areas increases toward the front end, relative to the insertion direction.
To sum up the advantages of the inventive solution, it can be said that it obviates the requirement for additional form ribs or steel grates so that the borehole does not need to be created enlarged, and mortar and expended energy can be saved during the creation of the borehole, as well as working time. Also, during the manufacture of the anchor rod as such, steps such as for attaching a grate can be saved, thus resulting in a cost savings.
The geometry of the present invention permits cleaning of the borehole, and damage to the surfaces or to the coating provided on same of the function-relevant surfaces is prevented during placement of the anchor rod.
The wall strength of the cured mortar shell varies due to the areas. An anchor rod designed according to the invention with a plurality of areas that adjoin in a circumferential direction, therefore, has the characteristic quality that the cured mortar shell is split in precisely defined locations, which results in superior post-expansion properties of the system.
Particularly advantageous is a friction-increasing coating provided on the shaft in the form of a shrinkdown plastic tubing. In combination with a preferably hexagonal shaft cross-section, this achieves that the coating of shrinkdown plastic tubing cannot twist relative to the shaft, that a very good blending of the mortar can be attained when it is entered by means of a percussion drill, and also a very good disintegration of the filler material.